The formation of ice on aircraft wings, propellers, engine inlets, etc. has been a problem since the earliest days of heavier-than-air flight. Any accumulated ice adds considerable weight, and changes the airfoil or inlet configuration making the aircraft much more difficult to fly and in some cases has caused the loss of aircraft. In the case of jet aircraft, chunks of ice breaking loose from the leading edge of an engine inlet housing can severely damage turbine blades or other internal engine components and cause engine failure.
Many attempts have been made to overcome the problems and dangers of aircraft icing. For example, proposals have been made, as described in U.S. Pat. No. 2,135,119 to mechanically vibrate external surfaces to break ice loose, or, as described in U.S. Pat. No. 3,549,964 to generate electromagnetic pulses in the aircraft skin to break ice loose. These systems, however, tend to be heavy and complex and to only remove existing ice, rather than prevent ice formation.
Heating areas of the aircraft prone to icing has been suggested many times. The heating ranges from microwave heating as suggested by U.S. Pat. No. 4,060,212 to feeding hot gases through holes in the skin, as suggested by U.S. Pat. No. 4,406,431, to resistance heating of the surfaces (U.S. Pat. No. 1,819,497) to actually burning fuel adjacent to ice-prone surfaces, as described in U.S. Pat. No. 2,680,345. While each of these methods have some advantages, none has been truly effective.
One of the most common anti-ice techniques has been the ducting of hot gases into a housing adjacent to the likely icing area. Typical of the patents describing such hot gas techniques are U.S. Pat. Nos. 3,057,154; 3,925,979; 3,933,327 and 4,240,250. In each case, the hot gas conduits simply dump hot gases into a housing, such as the leading edge of a jet engine housing or a wing leading edge. While often useful, these systems are not fully effective due to the low quantity of hot gases introduced relative to the mass of air in the housing, the heating effect tending to be limited to the region near the hot gas introduction point, and the complexity of the hot gas duct system.
Thus, there is a continuing need for improving aircraft icing prevention and removal systems having greater efficiency and mechanical simplicity.